The present invention relates to a circuit device.
Electronic circuit devices conventionally include electronic circuits installed on a metal-based circuit board. The circuit board is bonded on a heat sink (base substrate), which is used to transfer heat. FIG. 1 is a cross-sectional view briefly schematically showing a conventional circuit device. A circuit element 6, which is a heat-generating body, is adhered to a circuit board 3 with solder 5, and the circuit board 3 is adhered to a heat sink 8 via an adhesive layer 7. When the circuit board 3 and heat sink 8 are adhered by means of the adhesive layer 7, the adhesive layer 7 may harden such that the circuit board 3 is in an inclined state relative to the heat sink 8. This causes the thickness of the adhesive layer 7 to become uneven and reduces the thermal transfer efficiency between the element 6 on the board 3 and the heat sink 8. Moreover, the thermal expansion difference increases between the board 3 and the heat sink 8 such that cracks are generated in the adhesive layer 7 so as to cause concern that the board 3 may separate from the heat sink 8. To address this problem, Japanese Laid-Open Patent Publication No. 5-121603 describes art in which a spacer is provided between the circuit board 3 and the heat sink 8 so as to make the adhesive layer 7 have a uniform thickness.
FIG. 2 is a schematic cross-sectional diagram of a hybrid integrated circuit device introduced in the above publication. A circuit element 6, which includes a heat-radiating body such as a power transistor or the like, is fixed to a board 3 with solder 5. Spacers 50 are mixed into an adhesive layer 7 and applied to the heat sink 8. The board 3 is adhered to the heat sink 8 by means of the spacers 50. The spacers 50 are formed from a material that has satisfactory thermal conductivity and include, for example, metal grains having the same diameter or short glass fibers having the same length.
The circuit device of FIG. 2, however, can not ensure sufficient friction force between the board 3 and spacers 50 and between the spacers 50 and the heat sink 8 when the board 3 is adhered to the heat sink 8. Therefore, the board 3 is unstable with regard to external forces when the adhesive layer 7 is cured such that the board 3 may easily move. Accordingly, positioning of the board 3 is difficult. Furthermore, there is a possibility that the board 3 may be displaced from its designated position on the heat sink 8 and be fixed at that position.